All shades of opinion are in denial about the magnitude of the environmental challenge facing us. Ou

During the present century, human beings are likely to experience a change in the planetary environment unlike any in history. Climate change is irreversible, and accelerating fast. No one, apart from a few cranks speaking on behalf of the Bush administration, doubts that global warming is a side effect of human activity. Accumulating scientific evidence suggests strongly that climate change is happening on a larger scale and more quickly than was suspected even a couple of years ago. Observable processes such as the melting of the Antarctic ice cap point to rising sea levels that will wipe out much of the world's arable land and flood many coastal cities. The face of the planet is changing before our eyes.

The message of science is clear: humans will soon find themselves in a world different from any they have ever lived in. Altering our way of life to cope with these conditions will be phenomenally difficult - if it can be done at all. Yet all sections of opinion are in denial regarding the scale of the shift and the magnitude of the challenge it poses. Mainstream politicians and green activists differ on many points; but they all believe that climate change can be halted or rendered innocuous, if only we adopt the right policies. They are at one in rejecting the fact that runaway climate change is a result of the toxic mix of rapidly growing human numbers with worldwide industrialisation. Across the whole political spectrum there is a refusal to face up to this reality. This is nowhere clearer than among the Greens, who persist in a delusional faith that sustainable development and renewable energy can save the day.

In this consensus of denial, there are some who tell us not to worry. So-called "sceptical environmentalists" suggest that the scientific consensus is not to be trusted, and counsel inaction until the damage done by climate change is undeniable. That is the view of Nigel Lawson, who recently advised a business-as-usual strategy. Preparing for climate change is costly and troublesome, the former chancellor said, and we should alter our way of life only when the evidence is incontestable. The trouble with this view is that climate change is not doom-mongering speculation: it is already happening, and it is foolish to shut one's eyes and hope it will go away. If it takes the abrupt and radical form that many scientists believe is now likely, it will have disastrous effects on the lives of millions - possibly billions - of people.

Under the leadership of David Cameron, Lawson's own party is not so complacent, but it, too, is in denial. Cameron talks lightly of "green growth", and has demonstrated the seriousness of his environmental commitment by riding a bicycle and installing a wind turbine on the roof of his house. The underlying assumption of his approach is that the crisis can be tackled without doing anything difficult or unpopular. The facts tell a different story. Wind power is not terribly efficient, and certainly cannot replace fossil fuels as the source of most of our energy. Even if combined with other types of renewable power such as solar and geothermal and implemented together with rigorous policies of energy conservation, the output of the hideous windfarms springing up across the country could not meet the rising demand for energy that goes with current patterns of economic growth.

Nor would a large-scale shift to renewable energy in Britain have any perceptible impact on global warming, which is far more affected by emissions originating in China, India and the United States. It might be argued that Britain should do what it can to reduce emissions regardless of the behaviour of other countries; but there is only one existing technology that can provide energy on the scale Britain needs while reducing its production of greenhouse gases, and that is nuclear power - which is highly unpopular. Images of Chernobyl and its aftermath are potent antidotes to rational thought, even if all they tell us is how horribly unsafe nuclear technology was in Soviet times. We live in a culture in which personal emotional comfort counts for more than any objective assessment of risks and consequences, and public attitudes to nuclear power reflect this. As a type of psychotherapy for shopped-out consumers troubled by occasional pangs of environmental guilt, renewable energy may be quite effective. As an appropriate response to environmental crisis it is a non-starter.

It may be too much to ask from electorates that they confront unpalatable environmental realities. This month Tony Blair declared that nuclear power was "back on the agenda with a vengeance". In a speech to the Confederation of British Industry, he suggested that the replacement of nuclear power stations - in conjunction with "a big push on renewables and a step change on energy efficiency" - must be considered as part of Britain's long-term energy strategy. Blair is to be congratulated on attempting to thrust the real energy options we face into the forefront of public debate. His intervention comes near the end of his political career, however, and, given his disastrous role in the Iraq war, nothing that he says on any controversial issue will be taken seriously - even if, as in this case, it deserves to be.

In speaking out in support of nuclear power Blair runs up against the feel-good mentality: most people want to believe that the environmental crisis can be solved by policies which involve no risk - to them or anyone else. Green thinking encourages this mentality. For example, the Kyoto treaty may have symbolic value in acknowledging the anthropogenic origins of global warming, but it hardly deserves the iconic status it is given by the green lobby. None of the big three producers of greenhouse gases has signed up to it, and even if it were fully implemented it would do very little to alter the climate shift that is already under way. Above all, such a treaty cannot halt the stampede to industrialisation that is the human cause of global warming.

Global warming as we know it today is a by-product of the industrial revolution. The temperature of the planet has been rising since roughly 1800, when the use of fossil fuels began on a large scale. Industrialisation and fossil-fuel use are different sides of the same process, and it is the rising demand for energy that is fuelling global warming. Our present industrial civilisation began with coal, and it may well end there. Oil gained in importance in energy use throughout the 20th century, but as light crude oil becomes scarcer and more expensive, industrial societies are beginning to look to other fossil fuels which are still abundant - notably coal and tar sands. If the oil price remains high over the coming years, market processes will make these other fuels economically viable, and many economists think this will solve our problems. They have failed to factor in the increase in global warming that such a shift will entail. There are new technologies that can make coal cleaner, and we would be well advised to develop them further if we want to limit its environmental risks; but a global shift from conventional energy sources to coal and tar sands is bound to increase greenhouse gases. While shifting to other fossil fuels may make economic sense, there is nothing in the operation of the price mechanism that registers costs to the planet as a whole.

Green activists say they want a new global economic system in which fossil fuels play a much smaller part and damage to the planet is fully accounted for, but here again we are in the realm of denial. The type of energy-intensive industrial economy that is being adopted in India and China is clearly unsustainable. At the same time there is not the remotest prospect that the rush to industrialisation will be abandoned. The ruling elites of China are well aware of the hideous damage that their breakneck industrial growth has done to the country's fragile natural environment - far more so than the western investors who gush on about the Chinese economic miracle. China's rulers also know they cannot risk slowing economic expansion. Even with the one-child policy and rapid ageing, China's population will continue to grow for the next 50 years, and the hundreds of millions who are moving from rural areas to towns will need jobs, housing and transport. If enormous social upheaval and political instability are to be avoided, economic expansion must continue whatever the environmental consequences. The same is true in India, and throughout the poor countries of the world.

Worldwide industrialisation has an overwhelming momentum that cannot be stopped by political means. Part of this momentum undoubtedly comes from continuing population growth, but any mention of growing human numbers is now taboo in environmental debate. In the affluent west, religious fundamentalists, neoliberal missionaries for free markets, development economists and the few remaining Marxists are as one in denouncing the idea that there can be too many people. Curiously, this view has not been adopted in poor countries. China, Egypt, Iran, India and many other developing countries have population policies. In per-capita use of resources, it is the richest countries that are most overpopulated, and this is often used to suggest that it is distribution of resources rather than the global human population that really matters. The inequalities are real and troubling. Even so, no redistribution of resources could enable the earth to sustain over the long term the human numbers projected for the second half of the present century, or even those that exist today.

The present human population of more than six billion people is supported by a type of industrialised farming that relies on rapidly depleting supplies of petroleum. Contrary to the romantics among greens who look back with nostalgia to an imaginary peasant culture of harmony with nature, farming has always been, ecologically, a highly disruptive human activity, and this remains true today. It is mainly the expansion of agriculture, not industry, which is destroying the Amazon rainforest; but agriculture everywhere is critically dependent on oil-based fertilisers. The green revolution was at bottom a process whereby food was extracted from petroleum. A human population of roughly nine billion - the UN estimate for the world in 2050 - would be even more dependent on fossil fuels, with all the harmful effects on global climate.

In a century or so, human numbers may decline as falling fertility spreads throughout the world. In the meantime there is a bottleneck, and governments are scrambling to secure control of the world's remaining reserves of oil and natural gas. The resource war that is being fought for oil in the Gulf is likely to be one of many in the coming century, and will be accompanied by conflicts over fresh water. Population growth, resource war and climate change are intertwined. Without a smaller human population there can be no solution to the environmental crisis, and one way or another human numbers are sure to fall. Greens shy away from these facts, and insist that climate change and conflict over natural resources can be avoided by adopting a low-tech lifestyle. But organic farms and windmills cannot stop the destruction of the natural world, or support the present human population.

Rather than flirting with the fantasy of a low-tech society we need to focus on high-tech solutions to environmental crisis. Technology cannot change the human condition. It cannot repeal the laws of thermodynamics, or make human beings less prone to folly or illusion than they have always been. It cannot even deflect the current wave of climate change, which will go on for centuries whatever we do now. What technology can do is help us cope with the abrupt alteration in the planetary environment that human activity has triggered - a process of adjustment that is sure to be forbiddingly difficult. We cannot stop climate change. If we make the most of technologies that limit the need for fossil fuels we can avoid accelerating it.

James Lovelock has argued that we need to move away from traditional modes of farming to the production of synthetic foods, and it seems to me that, here as elsewhere, he points a way forward. Lovelock is best known for his support of nuclear power - a view I have shared since 1993, when I endorsed it in my book Beyond the New Right. Despite Chernobyl, the risks of nuclear energy to human beings have been greatly exaggerated. Just as important, nuclear power is vastly less harmful to the non-human environment than fossil-fuel extraction. For this reason alone, green activists should support it. Yet they remain deeply hostile to high-tech solutions, and part of the reason may be their well-founded suspicion of the idea that humans can master nature by means of technology.

In the past, high technology has been linked with Promethean philosophies that seek to subject the natural environment to human will. This was the philosophy that produced ecological catastrophe in the former Soviet Union and in China during the Maoist era - and which, in a different ideological guise, is continuing the destruction of the environment in those countries. In western countries, the Promethean view is to be found mainly on the right, among neoliberal boosters of the free market and Bushite deniers of climate change. Given this background, it is hardly surprising that green movements should reject technical fixes, but by doing so they have become part of the problem rather than its solution.

Today, high technology offers the only way the human ecological footprint on the planet can be reduced. Nuclear power has risks, not least of terrorist attack; but it is vastly less harmful to the planetary equilibrium than the continued reliance on fossil fuels that is the realistic alternative. The environmental dangers of genetically modified crops are as yet unknown, so it is right to resist their use at present; but it is not difficult to envisage a time when they could be less destructive of the natural world than the further expansion of petroleum-based intensive agriculture. Far from rejecting these new technologies, we should be developing and improving them - not in order to further our domination of nature, which has always been an illusion, but as ways of retreating from our hugely overextended position in the planetary system. Green movements look to political solutions to the environmental crisis. For them, its source is in a defective economic system and in abuse of corporate power. However, the planetary rebalancing that is under way cannot be prevented by any transformation of human society, however revolutionary. Adapting to the situation requires political decisions, but there is no political solution to the problems we face. The human species has overshot the planet's resources, and it will have to use all its technological ingenuity if it is to avoid catastrophe.

It may be that the shift in habits of thinking that is needed is beyond human powers. We owe our evolutionary success partly to our capacity for denial. Blind hope has often been more useful than a rational estimate of danger in promoting human survival. Today the tendency to shut out from conscious thought the dangers we face has itself become dangerous, but it is a tendency that is encouraged in a culture which prizes emotional comfort over everything else. In the worst-case scenarios that are now looking increasingly realistic, the result could be a change in the way we live that has no precedent in human experience.

Abrupt climate change seems an apocalyptic prospect, and rather than face up to it and do what can be done to mitigate its effects, humanity may well opt to let it run its course. It is only in human terms that climate change can be viewed as apocalyptic, however. In the life of the planet, it is normal. A dramatic climate shift took place 55 million years ago, at the start of the Eocene era, in which most of the species that then existed became extinct. The planet revived and became the richly diverse biosphere human beings are at present destroying. The environmental change that the world is undergoing is another such shift. Much biodiversity will be lost, but the earth will renew itself. Life will continue and will thrive - whether or not humans are around to see it.